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Hot sauropod news, part 2: A new look for Sauroposeidon

September 5, 2012

YPM 5449, a posterior dorsal vertebra of Sauroposeidon, from D’Emic and Foreman (2012:fig. 6A and C).

Another recent paper (part 1 is here) with big implications for my line of work: D’Emic and Foreman (2012), “The beginning of the sauropod dinosaur hiatus in North America: insights from the Lower Cretaceous Cloverly Formation of Wyoming.” In it, the authors sink Paluxysaurus into Sauroposeidon and refer a bunch of Cloverly material to Sauroposeidon as well. So in one fell swoop Sauroposeidon goes from being one of the most poorly represented Early Cretaceous North American sauropods, based on just four vertebrae from a single individual, to one of the best-known, most complete, and most widespread, based on at least seven individuals from Texas, Oklahoma, and Wyoming.

The web of connections among the different sets of material is complex, and involves the Sauroposeidon holotype OMNH 53062 from the Antlers Formation of southeastern Oklahoma, the type and referred material of Paluxysaurus from the Twin Mountains Formation of northern Texas described by Rose (2007), sauropod material from the Cloverly Formation of north-central Wyoming described and illustrated by Ostrom (1970), and UM 20800, a scap and coracoid newly excavated from one of Ostrom’s old quarries. D’Emic and Foreman argue that (1) the Cloverly material is referable to Sauroposeidon based on the shared derived characters of a juvenile cervical, YPM 5294, and the Sauroposeidon holotype, and (2) Paluxysaurus is not distinguishable from the Cloverly material and in fact shares several autapomorphies with the Cloverly sauropod. Which means that (3) Paluxysaurus is Sauroposeidon.

But that’s not all! All the new material suggests different phylogenetic affinities for Sauroposeidon. Instead of a brachiosaurid, it is now posited to be a basal somphospondyl. That’s not super-surprising; as we noted back in 2000 (Wedel et al. 2000), if Sauroposeidon was a brachiosaurid it had evolved some features in parallel with titanosaurs, most notably the fully camellate internal structure of the cervical vertebrae. And it also makes sense because other basal somphospondyls include Erketu and Qiaowanlong, the cervicals of which are similar to Sauroposeidon in some features. D’Emic and Foreman (2012) cite a forthcoming paper by Mike D’Emic in the Journal of Systematic Paleontology that contains the cladistic analysis backing all this up, but the case based on comparative anatomy is already pretty strong.

If anyone is unconvinced by all of these referrals, please bear in mind that we haven’t heard the whole story yet, quite probably for reasons that are outside of the authors’ control. I am inclined to be patient because I have been in that situation myself: Wedel (2003a) was intended to stand on the foundation of evidence laid down by Wedel (2003b), but because of the vagaries of publication schedules at two different journals, the interpretive paper beat the descriptive one into press by a couple of months.

Mid-cervical originally described as Paluxysaurus, now referred to Sauroposeidon, from Rose (2007:fig. 10).

Anyway, if anyone wants my opinion as “Mr. Sauroposeidon“, I think the work of D’Emic and Foreman (2012) is solid and the hypothesis that Paluxysaurus is Sauroposeidon is reasonable. So, if I think it’s reasonable now, why didn’t I synonymize the two myself? Partly because I thought there was a pretty good chance the two were not the same, based mostly on FWMSH 93B-10-8 (which I referred to as FWMSH “A” in Wedel 2003b, since I had only seen in on display without a specimen number), which I thought looked a lot more like a titanosaur cervical than a brachiosaur cervical. But of course I thought Sauroposeidon was a brachiosaur until a couple of months ago, and if it ain’t, and if brachiosaurs and basal somphospondyls have similar cervicals, that objection is considerably diminished. And partly because I’ve had other things to be getting on with, and stopping everything else to spend what would realistically be a few months looking into a possible synonymy (that I didn’t strongly suspect) wasn’t feasible in terms of time or geography. So I’m glad that D’Emic and Foreman have done that work, and I’m excited about the new things they’ve uncovered.

And I’m honored to bring you a new life restoration of Sauroposeidon by uber-talented Bob Nicholls, which we think is the first to show Sauroposeidon in its new guise as a basal somphospondyl. Click through for the mega-awesome version.

Same critter, different views. If anyone wants to GDI this baby, you now have everything you need. Many thanks to Bob for permission to post these and the following making-of images. Please visit him at Paleocreations.com to see a ton of awesome stuff, and give him some love–or at least a few thousand “likes”–on Facebook.

This is Bob’s first foray into 3D modeling, but you’d never know from the quality of his virtual sculpt. And let me tell you, that dude works fast. He sent this initial version, showing Sauroposeidon as an attenuated brachiosaur (sorta like this) on August 23, to solicit comments from Mike and me.

I wrote back and let Bob know about the new work of D’Emic and Foreman, and suggested that he could probably be the first to restore Sauroposeidon as a somphospondyl. Mike and I also voiced our opposition to the starvation-thinned neck, and Mike suggested that the forelimb was too lightly muscled and that the ‘fingers’ were probably too prominent. The very next day, this was in our inboxes:

I wrote back:

Whatever Sauroposeidon was, its neck was fairly tall and skinny in cross-section. It looks like the neck on your model sort of tapers smoothly from the front of the body to the head. I think it would be much narrower, side-to-side, along most of its length, and would have a more pronounced shoulder-step where it met the body.

The bottom view is very useful. It shows the forefeet as being about the same size as the hindfeet. AFAIK all or nearly all known sauropod tracks have much bigger hindfeet than forefeet. Certainly that is the case with Brontopodus birdi, the big Early Cretaceous sauropod tracks from Texas that were probably made by Sauroposeidon. The forefeet should be about 75-80% the width of the hindfeet, and only about half a long front-to-back. Even if you don’t quite get to those numbers, shrinking the forefeet a bit and subtly up-sizing the hindfeet would make the model more accurate.

Mike’s commentary was much shorter–and funnier:

I like how freaky it looks. It looks WRONG, but in a good way.

Bob toiled over the weekend and came back with this subtly different, subtly better version:

I had one more change to recommend:

I’m sorry I didn’t suggest this sooner, but it only just now occurred to me. With the referral of Paluxysaurus and the Cloverly material to Sauroposeidon, we now have dorsal vertebrae, and they are loooong, much more similar in proportion to the dorsals of Brachiosaurus altithorax than those of Giraffatitan brancai. So, as much as I like the compact little body on your Sauroposeidon, I think it was probably fairly long in the torso. You probably already have Mike’s Brachiosaurus paper [Taylor 2009] with the skeletal recon showing the long torso–in the absence of an updated skeletal recon for Sauroposeidon, I’d use Mike’s Figure 7 as a guide for reconstructing the general body proportions.

Bob lengthened the torso to produce the final version, which is the first one I showed above. He sent that over on August 29–the delay in getting this post up rests entirely with me.

So. It is still very weird to think of “my” dinosaur as a somphospondyl rather than a brachiosaur. I had 15 years to get used to the latter idea. But suddenly having a lot more material–essentially the whole skeleton, minus some stinkin’ skull bits–is pretty darned exciting, and the badass new life restoration doesn’t hurt, either.

Now, would it be too much to wish for some more Brontomerus?

References

D’Emic, M.D., and B.Z. Foreman. 2012. The beginning of the sauropod dinosaur hiatus in North America: insights from the Lower Cretaceous Cloverly Formation of Wyoming. Journal of Vertebrate Paleontology 32(4): 883-902.

22 Responses to “Hot sauropod news, part 2: A new look for Sauroposeidon”

This is odd: Rose compared most of this material explicitly. I’ve not read the new paper, so I do not know how they deal with Rose’s differentiation, but Rose’s does seem weak in that the features (mostly laminar) may be variable. I continue to doubt the functional utility of laminae shape, position and size as viable diagnostic characters for naming new taxa.

There is lots of uncertainly in the reconstruction. Mainly from the fact that the material comes from multiple individuals which may not be the same size. That said, it should hopefully give some idea of what ”Paluxysaurus” looked like. I haven’t got a copy of D’Emic, Foreman. 2012, the posterior dorsals shown above look quite different to the posterior dorsal referred to Paluxysaurus by Rose 2007.

But can we have two boos, please, one each for the journals involved in this story? JVP’s figures for the new D’Emic and Foreman paper are monochrome, which really should not be acceptable in 2012; and PE’s for the Rose paper are just horribly tiny and blurry, Medium Bigfoot at best. Trying to do meaningful comparisons based on these inadequate illustrations is pretty futile.

I haven’t got a copy of D’Emic, Foreman. 2012, the posterior dorsals shown above look quite different to the posterior dorsal referred to Paluxysaurus by Rose 2007.

I didn’t show all of D’Emic and Foreman figure 6, but it has Paluxysaurus dorsals at the bottom and they look pretty similar to the Cloverly verts, especially in the shape of the neural spine. If you need a copy of D’Emic and Foreman (2012) and don’t have access, I’d say write to Mike D’Emic and ask for a copy. He’s always struck me as a generous guy.

Any chance that the western critters turn out to be adult Astrodon?

I strongly doubt it. ALL of the cervicals from the Arundel are proportionally short, so either there is some kind of freaky bias against the preservation or collection of even fragmentary long cervicals, or Astrodon was rather short-necked. Also, the Astrodon cervicals have fairly thick, robust walls. They’re built like juvenile Apatosaurus and Camarasaurus cervicals. In contrast, the juvenile Sauroposeidon cervical from the Cloverly (YPM 5294) is from a comparable ontogenetic stage (based on small size and not even a hint of neurocentral fusion) but the bone is extremely thin and the whole vert gives the appearance of having been carved from next-to-nothing by Middle-Earth elves. It already has a very high ASP (er, based on some photos of the broken faces at mid-centrum that I haven’t gotten round to publishing) and the big plate-like parapophyses that characterize adult Sauroposeidon cervicals. Neither feature is present in Astrodon.

As long as I’m wishing for more Early Cretaceous North American sauropod material, I would love for someone to find some adult Astrodon vertebrae so I can see if my prediction about their relative robustness (compared to Apatosaurus and Camarasaurus) is right.

It’s looking like sauropods evolve more slowly than other dinosaur groups or can their be some lumping going on. Our new basal macronuran is certainly close to BYU’s “Moabosaurus,” but our associated dromaeosaurs, iguanodonts, and ankylosaurs are clearly different, more basal genera, than those found with “Moabosaurus.” Another test of our working hypothesis.

Will be cool to see if we eventually find Sauroposeidon over in this part of the country, and Astro out West.

Agreed! Especially since Sauroposeidon seems to have ties to some of the titanosauriforms from the Early Cretaceous of Europe. At least, there are some vertebrae from the Isle of Wight with very high, Sauroposeidon-like ASPs, and the “Angloposeidon” cervical (MIWG.7306) is still more similar to Sauroposeidon (even the new, expanded Sauroposeidon) than it is to anything else. And if “sauroposeidonids” roamed from the American West to England, they probably went through Maryland. And there’s no reason why “astrodonts” might not have roamed just as widely. Still a ton of interesting things to be learned about these enigmatic Early Cretaceous sauropods.

Even though it’s labeled as a somphospondyl, the Bob Nicholls model (all versions of it) looks like a classic brachiosaur in just about every respect. That said, a lot of cretaceous macronarians blur the lines between the two groups.

I wouldn’t be surprised if “sauroposeidonids” end up clustering as highly derived brachiosaurs, though Paluxysaurus has some oddly Euhelopus-like femora (bent back at the 4th trochanter) despite not a hint of bifid neural spines anywhere on its verts. And things like Venenosaurus and Tastavinsaurus look very reluctant to let go of their brachiosaur ancestry OR embrace a somphospondyl one.

It would be interesting to see how all of these tall, gracile forms relate with Janenschia, which also has the Euhelopus-like kink in the femur, but is far more robust and stocky than either brachiosaurs or euhelopodids. Fraas (1908) illustrated an undescribed sacrum (fig. 10) and a Brontomerus-like or Tastavinsaurus-like ilium (fig. 11) which look like they could well belong to Janenschia or some other robust titanosauriform.

Even though it’s labeled as a somphospondyl, the Bob Nicholls model (all versions of it) looks like a classic brachiosaur in just about every respect. That said, a lot of cretaceous macronarians blur the lines between the two groups.

Well, exactly. Item 1: a good skeletal reconstruction of Euhelopus doesn’t look that different from a brachiosaurid, proportionally, even though there have been some changes “under the hood”. Item 2: Sauroposeidon/Paluxysaurus is brachiosaurus-y enough to have come out as a brachiosaurid in the analysis of Rose (2007)–and might again in future analyses. That’s not a criticism of Mike D’Emic’s work, more a realization that (Item 3): the definition of Somphospondyli is taxa closer to Saltasaurus than to Giraffatitan, so if something is a titanosauriform, it has to be one or the other. The most basal brachiosaurid and the most basal somphospondyl are literally separated by a single node.

So I’m not surprised or broken up about a lot of these supposed brachiosaurids turning out to be somphospondyls. They’re still landing only a node or two away, which is just not that big a deal, especially when things are so fluid in this part of the tree right now anyway.

That’s true. That particular area of sauropod taxonomy is quite a mess at this point… Brachiosaur or Somphospondylian, it’s still a toss-up. I was just a bit shocked at how the Nicholls model looks a lot more like Giraffatitan than Euhelopus (or at least the GSP version of Euhelopus, which aside from the low grade of the dorsal column and scapula angle, seems pretty accurate.)

It looks pretty clear to me that there are still quite a few steps to go from “most basal barely brachiosaurid somphospondyli” to full-fledged Euhelopodidae (which is what most people seem to mean when they say ” basal somphospondyli”). The bifid spines in the lower neck, the bizarre pes phalanges, the tall neural arches and modest neural spines, had yet to emerge. Probably still gotta go through intermediate forms like Tastavinsaurus, Chubutisaurus, Ligabuesaurus, Janenschia, Dongyangosaurus and Huanghetitan to get there. There’s an obscure set of cervico-dorsal vertebrae (41HIII-0008) found in Henan province (Lu, et. al. 2009b) that may belong to Huanghetitan and have low bifid spines, and Dongyangosaurus already has the high neural arches, extremely oversized front ilium and slimmed-down pubes that characterize more advanced somphospondyli like Euhelopus. But a more basal somphospondylian like Ligabuesaurus doesn’t even come close in dorsal morphology.

All the same, it’s a gorgeous model of Sauroposeidon. Hats off to Bob. And since the posture and form can easily pass for a “classic” brachiosaur, there’s no need for further modifications if it turns out D’Emic was incorrect. At this point I suppose whichever clade you restore it as resembling will be more a matter of personal taste http://paleo-king.deviantart.com/#/d5duc59 than anything else. At least until more research is done.

What would Astrodon johnstoni cervical vertebrae look like, again? It is based on teeth. I think I made a big point of this in 2005, when I argued, among many things, that

1. The types of Pleurocoelus and Astrodon are not congruent with one another,
2. that the dental morphology of the latter are not technically exclusive of johnstoni,
3. that the types of nanus and altus are not only juveniles, but
4. distinct from one another on a morphological level despite close size, suggesting some form of taxonomic distinction rather than conspecificity — which is itself especially relevant when
5. you consider than variation in limb structure can lead to “generic” distinction among sauropods, such as the material from the Wealden. This leads me to argue that
6. Astrodon johnstoni should not be used for the Arundel sauropod material, and that Pleurocoelus — one of its species, rather, on specific details — should be the nomenclature used, contra Tidwell and Carpenter’s argument, which they themselves agree is not quite that compelling (pg.82).

[…] a lot more Sauroposeidon material these days than there used to be, thanks to the referral by D’Emic and Foreman (2012) of Paluxysaurus and Ostrom’s Cloverly material and the new Cloverly material to my […]

[…] holds what I once inferred to be the back half of C7 and all of C8. Now that Sauroposeidon may be a somphospondyl rather than a brachiosaur, who knows what verts these are–basal somphospondyls have up to 17 […]

[…] of Sauroposeidon has a 125-cm centrum, and Sauroposeidon always comes out as a titanosauriform in phylogenetic analyses, including the one in the Dreadnoughtus paper. The estimated 2.5-meter femur of Argentinosaurus […]